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Author Topic:   Raising engine height on Montauk 170.
WT posted 02-05-2005 11:10 PM ET (US)   Profile for WT   Send Email to WT  
I have a 2004 Montauk 90 hp 4 stroke. Has anyone raised their engine from the stock/factory position to increase top speed?

It was suggested by Grand Island Marine that for optimum performance, all outboard motors can be raised to the highest mounting holes.


kingfish posted 02-06-2005 12:05 PM ET (US)     Profile for kingfish  Send Email to kingfish     
I'd humbly suggest that either you misunderstood someone at Grand Island Marine, or whoever made that statement needs to go back to school...

Motors can almost always, and usually should, be raised one or two holes from the bottom. That measurement however is secondary to the real determining factor, which is the relationship between the AV (anti-ventilation) plate on the motor, and the lowest point of the hull bottom extended back to the lower unit. The motor should usually be raised such that the AV plate is above (and as much as 1" to 1-1/2" above) the lowest point of the hull bottom, assuming a single motor and the motor mounted directly on the transom, no matter what hole that might be. Typically it is 1 or 2 holes up from the bottom.

WT posted 02-06-2005 12:27 PM ET (US)     Profile for WT  Send Email to WT     
Thanks Kingfish, perhaps I misunderstood. I'll call him on Monday to confirm.

I have 5 engine mounting holes. My engine is mounted on the 2nd hole from the top, meaning I can raise the motor 3 more notches. It seems to me based on eyeballing my AV plate that I can raise the motor 2 more holes the have the plate 1.5-2 inches above the bottom of the hull.

Has anyone with a Montauk 170 with a 90 4S raised their motor?

I am also going to install a Mercury 6 hp kicker in the next couple of weeks.



kingfish posted 02-06-2005 02:20 PM ET (US)     Profile for kingfish  Send Email to kingfish     
It's possible that given the conditions you describe, you could raise your motor all the way up; if it's too far, you'll know because you'll get blow out (ventilation) in rough water and on turns. If you've learned how to raise the motor, you can easily drop it back down a hole if it is too high. When you're trying to maximize performance by raising your motor as far as possible, you almost always need to have a high performance prop with plenty of cup, so you can still get traction.
timsr posted 02-09-2005 08:37 PM ET (US)     Profile for timsr  Send Email to timsr     
WT after you install that kicker motor I'd be interested on how you or the delaer did it and a few pics would be great. Thanks.


WT posted 02-09-2005 10:22 PM ET (US)     Profile for WT  Send Email to WT     

I hope to have the kicker installed by the dealer before the end of this month. I drop the boat off next Saturday.

I should have pictures soon after. I'm not even sure of the brand of stainless steel bracket they are using. The dealer says they have installed six of these kickers on Montauk 170's.


mikeyairtime posted 02-10-2005 09:27 AM ET (US)     Profile for mikeyairtime    
I'm going to raise my 90 4-stroke Merc on my 170 and am wondering if there's an easy safe way to accomplish it without an engine hoist. My last boat with a 130 Yamaha had slots for two of the holes so I could take two bolts out, loosen the other two and with a block under the lower unit crank up the trailer tongue. The Merc has 4 bolt holes.
AQUANUT posted 02-12-2005 08:57 PM ET (US)     Profile for AQUANUT  Send Email to AQUANUT     
ah yes ...what is the OPTINUM engine mounting height....
deja vu......
there are many many discussions in this forum on this issue.

there are those that have opinions based on personal knowledge taught to them by others...the text books..and personal experience. my opinion is based on all three..and the fact I mount engines on a daily basis....this is a deep subject and I personally avoid the pages of text explaing it properly...however...on the 2004 montauk 170 with 115 EFI 4 stroke I just sold to high sierra....i mounted the engine in the third hole from the top { the middle} of five total.. boston whaler installs it the second from the top..I prefer the middle...anti cav plate 3/4 above keel.

in reference to supporting engine...I use a fork lift with chain..however mercury has since rescinded that and advise via tech bulletin that a lifting eye on the crankshaft is to be used verses the lifting eye mounts on top of the engine..apparently they can fail. I also use a hydraulic outboard engine hoist at times.....the idea of blocking engine and cranking trailer tongue jack,,,,is not well thot..or an experienced approach...the addhessive attaching the engine bracket to the so strong that you will literally lift the boat and trailer..until it finally fails...a dangerous situation......also an engine can normally support the weight on the skagg..but adding the weight of trailer and hull...rescipe for diasaster.

justa boat rigger

Marsh posted 02-13-2005 06:19 PM ET (US)     Profile for Marsh  Send Email to Marsh     
I moved the engine to the middle hole of the 115 Merc 4s, on my '04 Montauk. Did it alone in my garage, while on the trailer. Balanced the motor on its skeg, held upright with chain to roof truss. Remove old bolts, adjust trailer jack, reinsert bolts in new holes. Really easy. Hardest part was scraping all the old silicone seal off the nuts/bolts in order to get a wrench on them. Never did get it all off. What a mess.


AQUANUT posted 02-14-2005 08:28 AM ET (US)     Profile for AQUANUT  Send Email to AQUANUT     
indeed helping support the engine by chain to the powerhead is "key"
davej14 posted 02-18-2005 09:11 AM ET (US)     Profile for davej14  Send Email to davej14     
I agree with Aquanut, if you have a marina nearby that has an engine lift it is worth the $$$ they would charge to help you with raising the motor. I've done this several times with my merc 75. The instructions on this site for using the trailer to raise the motor refer to slots on the lower bolt pattern and as you now know your motor (and mine) has bolt holes. You have to back the bolts nearly all the way out to clean them and the motor needs to be far enough from the transom to get your hand in there to clean it up and reapply silicone.

A tip from my mechanic is that he uses spray engine cleaner (gets it from walmart) to clean up the transom. It worked great.

Another tip, which I researched online and discussed with Boston Whaler, is that you should use only marine grade silicone rated for below the waterline to "bed" the bolts and motor bracket during reassembly. Do not be tempted to use 3m 4200 or even worse 5200 for this application. You are just creating a seal not glueing things together.

bigjohn1 posted 05-19-2005 07:56 AM ET (US)     Profile for bigjohn1  Send Email to bigjohn1     
Warren, while doing a search, I noticed this aging thread and wondered if you ever raised your engine and if you did, what you felt it contributed to the 170's ride. I am going to raise one or two holes as my Doelfin is still totally submerged when on plane. I am in the second hole right now just like you were. Have you (or anyone else) gone up any higher than the middle hole on the 170? Has anyone experienced any blowout when mounted in the middle hole (or higher)?
mikeyairtime posted 05-19-2005 08:33 AM ET (US)     Profile for mikeyairtime    
I raised mine two holes. I'm going to test it on Memorial day weekend. I'll let you know. I made two wooden channel guides and clamped them to the transom. They hold the motor centered and have a lip that keeps the motor against the transom but has about 1/10th of an inch clearance to let the motor slide. Then I did the lower the trailer tounge block the motor raise the tounge thing. It worked very well but utmost care is advised. I went up two holes because I have a permatrim trim tab that helps with cavitation and also because I tend to be impusive by nature.
WT posted 05-19-2005 11:20 AM ET (US)     Profile for WT  Send Email to WT     

I haven't raised my motor. When I brought my Montauk in for the installation of the kicker, my BW dealer advised against raising my motor.


LHG posted 05-19-2005 12:34 PM ET (US)     Profile for LHG    
If your new 170 won't do much over 42 mph, as is the case with the Optimax and 4-stroke, raising it to the third set of mounting holes won't do much for you, and besides you will need a $350 Laser II or High Five prop for it, as the SS Vengeance will probably blow out. If you have the faster 2-stroke 90, or a 115, it might be worth considering, with same prop upgrade.
mikeyairtime posted 05-19-2005 02:07 PM ET (US)     Profile for mikeyairtime    
We'll see, mine was dragging the trim tab through the water pretty badly when it was up on plane in the stock holes.
mikeyairtime posted 05-29-2005 09:10 PM ET (US)     Profile for mikeyairtime    
Well the jury is in. Raising the motor two holes from stock (one hole down from the highest position)worked wonders. It caused zero cavitation and improved the way the boat ran across the board. I'm no longer dragging my perma-trim trim tab through the water, it runs right on the surface where it should be. The boat is more responsive to trim, goes faster at any given RPM, planes sooner than before and got noticably better mileage.
bigjohn1 posted 05-30-2005 08:30 AM ET (US)     Profile for bigjohn1  Send Email to bigjohn1     
Thanks for the report Mikey, sounds like it did alot of good for you. What type of water are you running in? Also, I assume you are running the 18P Vengeance prop? No
blowout at all?
mikeyairtime posted 05-30-2005 01:39 PM ET (US)     Profile for mikeyairtime    
I'm running the stock 18 vengeance. It was calm running out and lumpy running home. If I over trimmed it I could make it cavitate and porpise but it would do that in the stock holes. Sharp turns were no problem. One note: I have a perma trim hydrofoil/trim tab which no doubt helps for cavitation. I thought I would need a new prop, now I know I don't.
montaukman posted 06-07-2005 08:55 PM ET (US)     Profile for montaukman  Send Email to montaukman     

Hi Everyone,

I measured my stock engine height positioning compared to the keel of the transom and it appears my cav plate is approx in line with the keel. I have the Tigershark foil so i will def need to raise the engine.

I am not sure if I will do one or two holes. It is currently mounted second from the top.

That being said and reading all the other posts and directions, i am curious about a few things.

1.)The bracket seems to be integrated to the engine(one piece) and is mounted to the transom via 4 bolts. if you raise the bracket and engine up, the bracket will over extend the top of the transom. Also, it will leave a sealant and trim edge. Am I missing something or is the engine separate from the bracket. Does rthe bracket stay put while the engine mounts higer or lower?

2.) Is it necessary to reseal the holes and bracket? What gets sealed?

3. There are four bolts on that hold the engine to the transom. As mentioned in an earlier reply, the merc 90 uses predrilled holes for adjusting, not slots so the concept of sliding the engine higher or lower eludes me. Don't all the bolts have to be removed completely and then you raise the engine/bracket. Clamping is mentioned for keeping the engine attached to the transon (when not using a hoist). How is this done. I imagine you need a hefty c-clamp.

The whole process in theory seems simple. I just don't see how, if at all, the engine separates from the bracket. that might answer some of my questions.

Thanks for any help. I put on my fins and i still have 25 hours before i have my maintenence done so I want to do this myself rather than wait till i eat up 25 hours.

Thanks again,


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